Solenoid actuators and generators and method of using same

ABSTRACT

Solenoid actuators capable of high speed operation and high efficiencies are disclosed. The solenoids, in the most efficient embodiment, are coupled to the driven member (i.e., load) through a spring (i.e., decoupled) which spring is selected (i.e., matching) to allow high initial acceleration of the armature, followed by deceleration of the armature near the end of the stroke as a result of the spring force, thereby minimizing i2R losses and minimizing loss in kinetic energy by armature impact at the end of the stroke. To effectively accomplish the decoupling and matching, various methods of latching the solenoid at the end of the stroke, while the energy stored in the spring is delivered to the load, are disclosed, as are methods for decreasing the solenoid current from a high initial value so as to minimize resistive power lost in the winding. Solenoid generators using the principles of the present invention are also disclosed.

United States Patent 1 Link et a1.

SOLENOID ACTUATORS AND GENERATORS AND METHOD OF USING SAME Inventors: William T. Link; Peer M. Portner, both of Berkeley, Calif.

Arkon Scientific Laboratories, Berkeley, Calif.

Filed: Apr. 26, 1971 Appl. No.: 137,230

Assignee:

References Cited UNITED STATES PATENTS 10/1959 3l7/DlG. 6 9/1947 317/151 2/1903 310/15 X 3/1970 Lawson, Jr

Snyder Warwick et al...,

Done et a1. 310/77 Dec. 11, 1973 Primary Examiner-James D. Trammell Attorney-Spensley, Horn and Lubitz [57] ABSTRACT Solenoid actuators capable of high speed operation and high efficiencies are disclosed. The solenoids, in the most efficient embodiment, are coupled to the driven member (i.e., load) through a spring (i.e., decoupled) which spring is selected (i.e., matching) to allow high initial acceleration of the armature, followed by deceleration of the armature near the end of the stroke as a result of the spring force, thereby minimizing i R losses and minimizing loss in kinetic energy by armature impact at the end of the stroke. To effectively accomplish the decoupling and matching, various methods of latching the solenoid at the end of the stroke, while the energy stored in the spring is delivered to the load, are disclosed, as are methods for decreasing the solenoid current from a high initial value so as to minimize resistive power lost in the winding. Solenoid generators using the principles of the present invention are also disclosed.

19 Claims, 19 Drawing Figures SOLENOID ACTUATORS AND GENERATORS AND METHOD OF USING SAME BACKGROUND OF THE INVENTION 1. Field of the Invention.

The present invention relates to the field of solenoid actuators.

2. Prior Art.

Solenoids are well-known electrical-mechanical devices for the conversion of electrical energy into mechanical work. The ordinary solenoid is comprised of a coil of wire (i.e., winding) formed around a frame, generally made of a magnetic material and an armature (i.e., plunger) made of the same magnetic material which may be attracted into closer relationship to the stationary portion of the solenoid by the passage of a current through the coil. Various forms of such solenoids are well-known and in use. In general, the plunger of a solenoid would be directly connected to the load or device to be actuated by the solenoid, the type of solenoid having been selected so as to have the required stroke. The size of the solenoid is then selected to give at least the minimum required force throughout the stroke, and if continuous or substantially continuous operation is required, to dissipate the heat generated within the solenoid. In the past, a solenoid design was considered complete and the solenoid adequate if the solenoid stroke was required for the particular application, the force created by the solenoid exceeded the force required by the load by a safe percentage at most or all points in the solenoid travel, and the heating within the solenoid was not excessive when operating under the required duty cycle.

It has long been recognized that the efficiency of solenoids for the conversion of electrical energy into useful work is very low and, therefore, solenoids have been used generally where efficiency in such sense, that is, usable work output for a given electrical input, is not a primary consideration, but instead where cost is the primary consideration. Byway of example, solenoids are commonly used in dishwashers and other appliances for such purposes as opening and closing valves to let water in and out, to shift gears, etc. By way of specific example, the valve following water to flow into a dishwasher is generally solenoid actuated and may be turned on by actuation of a solenoid for periods of perhaps 60 seconds at a time. The valve is commonly spring loaded so as to be self-closing upon termination of the power to the solenoid. Solenoid used for this application are designed to have a force sufficient to overcome the return spring in the valve and any friction between the various parts by a satisfactory margin, and to have a stroke sufficient to properly actuate the valve. Upon actuation of the solenoid, the moving part of the valve and the solenoid plunger accelerate toward the fixed portion of the solenoid, characteristically slamming against the fixed portion of the solenoid at the end of the travel. While useful work has been done in opening the valve, much of the mechanical energy produced by the attraction of the plunger by the fixed portion of the solenoid goes into kinetic energy in the plunger and valve moving parts, and is dissipated by conversion to heat upon slamming into the end of the solenoid. In addition to the resulting inefficiency, the resulting shock and vibration are not conducive to a long operating life for the solenoid and/or valve. Also, the actual opening of the valve requires only a fraction of a second,

whereas the valve is thereafter held open by application of full actuating current to the solenoid. Thus, although these are commonly alternating current solenoids so that the current will drop somewhat upon increase of the inductance of the solenoid coil in the actuated position, there will be a substantial current in the coil which will cause substantial heating in the coil throughout the ON period. Clearly through this portion of the cycle, the efficiency of the solenoid is zero since considerable heating results primarily from the PR loss in the solenoid coil, while no useful work is being done. The PR loss has been reduced in the past by increasing the amount of copper in the solenoid while increasing the cost of the device. For solenoids actuated from a direct current source, the efficiency is even worse, since the increase in inductance in the solenoid coil upon actuation of the solenoid does not result in any decrease in the current in the solenoid coil.

When a solenoid plunger is at its maximum extension, considerable current must be passed through the solenoid winding in order to properly magnetize the solenoid iron and to achieve the desired solenoid force. However, as the plunger moves from the fully extended position toward its withdrawn position (i.e., closed), the current required to adequately magnetize the solenoid iron decreases from the maximum and, when the solenoid plunger is in the fully actuated position, is only a very small percentage of the current required to magnetize the iron in the fully extended position. However, the usual application of solenoids involves connection of the solenoid winding to a constant voltage source which, after the initial transient, passes a constant current through the solenoid winding, independent of the position of the solenoid plunger. The current remains at the high level even after the plunger bottoms in the stationary portion of the solenoid when the current requirements to hold the plunger in that position are very low, and no further useful work is being done. Thus, it is apparent that the electrical power dissipated in the solenoid winding is far greater than it needs to be for proper actuation of the solenoid.

Solenoids used in applications as hereabove described are selected primarily because of their low cost and suitability to provide the desired actuating motion without regard to the actual efficiency of the device, since in such applications the electrical power available is substantially unlimited compared to the mechanical work which must be done by the solenoid. However, in other potential applications, solenoid efficiency may be a prime consideration, both because of the manner in which efficiency may be related to solenoid size and heating, and because of the amount of useful work which must be realized from a given amount of electrical energy. By way of example, in a battery operated pump, it would generally be desired to achieve the greatest pump output possible for a single battery recharging. This is especially true for airborne, space or portable applications. Heretofore, other actuators, such as D. C. motors have been used for such applications because the efficiency of prior art solenoids typically ranges as low as from 5 to 0.5 percent, and lower. In other applications, the speed of operation coupled with a high efficiency may be the primary application requirements.

In addition to PR losses and kinetic energy dissipation in solenoids, there are other sources of loss which in specific solenoids may be reasonably high also.

These additional sources of loss include eddy current losses and mechanical friction between the plunger and the stationary portion of the solenoid. These sources of inefficiency, however, are commonly understood and are generally considered as part of the solenoid design problem.

In applications requiring a fast acting solenoid, an initial high voltage may be applied to the solenoid winding to initially cause the current to flow in the winding. This is generally done by the discharge of a capacitor through the winding so that the high voltage on the capacitor drops as the current begins to flow. However, such schemes as are known in the prior art are not for the purposes of initially causing a high current in the solenoid which subsequently decreases, but instead are merely to cause the current in a solenoid having a substantial inductance to reach the desired substantially constant level as quickly as possible. By way of example, in US. Pat. No. 3,465,730 entitled Electronic Control Circuit For Electro Hydraulic Transducers, a scheme is disclosed for recovering the magnetic energy stored in the solenoid, upo'n opening of the solenoid coil, in a capacitor, and by subsequently discharging this capacitor to help cause the current to initially flow in another solenoid. However, it should be noted that when the plunger of a solenoid is in the withdrawn position, the energy stored in the magnetic field is simply the energy stored in the magnetic field within the solenoid iron, since the solenoid air gap is substantially zero at this point. This energy is relatively low since the solenoid iron has a high permeability. However, when the solenoid is first actuated with the plunger at its maximum extension, a sufficient amount of energy must be put into the solenoid to magnetize both the solenoid iron and the air gap. Thus, it is apparent that the energy recovered in the capacitor upon turning off the solenoid is substantially less than the energy which must be applied to a solenoid when first actuated in order to create the desired magnetic field within the solenoid and to achieve the maximum solenoid force. Clearly, this type of capacitive discharge does not cause a high initial current which tends to decrease as the plunger approaches the stationary portion of the solenoid but instead is simply an aid in decreasing the time constant in the current rise wave form upon actuation of the solenoid.

In summary, prior art solenoids (in the manner in which they are commonly used) are recognized as being convenient devices for such purposes as actuators which require a certain type of actuation, such as a short linear actuating stroke, in applications where efficiency of the actuating device is not a prime consideration. However, for those applications where efficiency and/or useful work output for a given size actuator must necessarily be high, solenoids have heretofore not been used, but other types of actuators, generally motors coupled to gear trains and the like, are instead used because of the low efficiencies herebefore achieved with solenoid actuators. Also, solenoid devices have heretofore not been used as generators for the practical conversion of mechanical energy into electrical energy.

BRIEF SUMMARY OF THE INVENTION Solenoid actuators which have a high efficiency and low actuation time, and circuits for energizing the actuators are disclosed'ln the preferred embodiment, the

solenoid plunger is coupled to the load through a spring (load decoupling) so that the solenoid plunger may move with respect to the load, thereby temporarily storing mechanical energy in the spring for later delivery to the load. (The manner in which the force exerted on the plunger is proportioned to the load is referred to as matching which is another aspect of the invention, that is, in certain specific embodiments related to the spring selection, but a spring is not essential to this aspect of the invention). This allows the solenoid plunger to be rapidly moved and latched in the actuated position. Since the required magnetomotive force to adequately magnetize the solenoid iron is much less in the actuated position than in the extended position, the current in the solenoid coil is reduced during the plunger travel to a relative low value when the solenoid is in the actuated position so as to grossly reduce the FR loss in the solenoid (i.e., current taper).

The coupling spring not only allows a shorter actuation time for the solenoid by allowing the solenoid plunger to move relative to and faster than the load (which reduces i R losses) but also stores the kinetic energy in the plunger so as to result in very little energy loss upon the collision of the plunger with the stationary portion of the solenoid. Since generally the spring force will initially exceed the usual solenoid force in the actuated position, various means of maintaining the plunger in the actuated position, are disclosed (latching). Also, a method and a circuit is disclosed for energizing the solenoid coil by the discharge of a capacitor which, in conjunction with a .diode trap," causes the current to taper in a fashion which reasonably well duplicates the ideal current wave form to properly energize the solenoid and to yield a minimum iR loss.

In summary, important aspects of the invention are decoupling, matching, latching and tapering" and the interaction of the plunger stroke with the magnetic field. These aspects alone are important and a number of them together in a particular application make obsolete the idea that the solenoid is not well suited for high speed, high efficiency and low weight applications. Also, using these principles, practical and efficiency solenoid generators may be built, as are further disclosed herein.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic representation of a prior art solenoid and the circuit for energizing the solenoid.

FIG. 2 is a schematic representation of a circuit of the present invention as used to energize the prior art solenoid of FIG. ll.

FIG. 2a is a curve illustrating the voltage wave form on the solenoid coil as the energizing capacitor 38 discharges.

FIG. 2b is a curve illustrating the current wave form in the solenoid coil 22 during the same time period as shown in FIG. 2a.

FIG. 3 is a schematic representation of the preferred embodiment of the present invention showing a solenoid coupled to a load through a spring and circuits for energizing the solenoid and clamping the solenoid in the actuated position.

FIG. 3a presents a graphical representation of the solenoid force and the coupling spring force for various positions of the solenoid plunger.

FIG. 3b is a curve illustrating the variation of plunger velocity as the plunger travels from the fully extended to the fully actuated positions.

FIG. 3c is a graphical illustration of the solenoid force for various positions of the plunger and an alternate form for the spring force characteristic of the coupling spring 52 of FIG. 3.

FIG. 3d is a curve illustrating the variation in plunger velocity between the fully extended and the fully actuated positions.

FIG. 4a shows on an expanded scale a part of the stationary portion of the solenoid and the facing surface of the solenoid plunger illustrating indentations on the plunger for purposes of latching the plunger in the fully actuated position.

FIG. 4b shows the solenoid parts of FIG. 4a in the fully actuated position illustrating the magnetic field concentration caused by the indentations in the plunger.

FIG. 5 is a curve illustrating the efficiency of a solenoid for producing output work as a function of external load force divided by the available magnetic force.

FIG. 6 is a schematic representation of the solenoid generator of the present invention.

FIG. 7a is a schematic represenation of the solenoid generator of FIG. 6 with the plunger and driving member in the withdrawn position.

FIG. 7b is a schematic representation of the solenoid generator of FIG. 7a with the plunger latched and the driving member in the extended position.

FIG. 7c is a schematic representation of the solenoid generator of FIG. 7b with the plunger in the extended position, thereby converting the energy stored in the coupling spring into energy stored in the magnetic field.

FIG. 7d is a schematic representation of the solenoid generator of FIG. 7c after which switch 92 is opened and switch 90 is closed, thereby converting the energy stored in the magnetic field into electrical energy stored in capacitor '78.

FIG. 8 is a graphical representation of the magnetic force and the spring force in the solenoid generator of FIG.'6 for various positions of the solenoid plunger.

FIG. 9 is an alternate embodiment using multiple solenoid generators in combination with a single electrical energy utilization means.

DETAILED DESCRIPTION OF THE INVENTION First referring to FIG. l, a schematic representation of a prior art flat faced solenoid and the circuit used to actuate the solenoid may be seen. The solenoid is comprised of a stationary member of soft iron having a coil 22 therein for creating a magnetic field 24 between the stationary iron 20 and the iron in plunger 26 connected to load 28. Load 28 is the load to be actuated by the solenoid, such as a valve, a pump or the like.

The solenoid is actuated from a direct current power source 30, which is connected to coil 22 through switch 32. Arcing and/or excessively high voltages at switch 32, upon opening the switch, are limited by resistor 34 which allows the current in coil 22 to temporarily continue to flow, thereby limiting the back EMF induced in the coil. Other devices may be used in place of resistor 34 such as, by way of example, a diode. Switch 32 and the switches to be hereinafter identified may be, by way of example, mechanical switches or electronic switches such as silicon controlled rectifiers or transistor switches.

A first method and structure for increasing the efficiency of a solenoid is illustrated in FIG. 2, and provides automatic current tapering for the solenoid. In this description of FIG. 2, it is assumed that the solenoid is to be actuated but need not linger in the actuated position for any substantial length of time. Power source 36 is used to charge capacitor 38 by closing switch 40 while switch 42 is open. When the capacitor 38 is charged, switch 46 is opened and the solenoid may then be actuated by closing switch 42. The voltage V is applied to coil 22 upon the closing of switch 42 shown in FIG. 2a. The voltage jumps substantially instantaneously to V where V is the voltage on capacitor 38 just prior to closing switch 42. When the switch is closed, capacitor 38 discharges through coil 22, causing a current I in the coil as shown in FIG. 2b. When the voltage on capacitor 38 drops to a value approximately equal to the IR drop in coil 22, current I stops increasing, and as the magnetic field caused by the current in coil 22 collapses, the voltage on the coil swings negative to a value equal to minus V,,, where V is the forward conduction voltage drop in diode 44. Thereafter,-the current I in coil 22 circulates through diode 44, steadily decreasing at a relatively rapid rate as the plunger 26 accelerates toward the stationary part of the solenoid. After the current has switched to diode 44, the capacitor 38 has no further effect on the circuit. When plunger 26 is in its fully actuated position (in contact with core 20) at time t,, the current I decreases more slowly, and at a substantially uniform rate, to zero. The initially rapid decrease of current I from its maximum value to its value at time 1, does not represent a corresponding collapse in the magnetic field in the solenoid, but rather represents a decrease in the magnetizing current required to maintain the field in the solenoid as the solenoid plunger moves toward the stationary portion of the solenoid and the air gap decreases. Thus, the flux in the solenoid at time t, will be substantially equal to that in the solenoid when current I is at its peak. However, since the plunger 26 is fully actuated at-time l, the leakage fields in the solenoid are at a minimum and the actual force generated by the solenoid will be as high or higher than that existing when the current was at its peak value.

The current decay after time t represents a collapse in the magnetic field in the solenoid, and after a collapse to a certain value at a return mechanism coupled to the load 28 overcomes the force of the solenoid and plunger 26 is returned to its extended position.

It is to be noted in FIG. 2b that the current I is at its maximum or near maximum values for only a very short period of time, and thereafter quickly decays to a much lower value at time t, as the plunger 26 accelerates toward the fixed portion of the solenoid. Thus, peak heating in the solenoid coil due to the FR loss therein occurs only for a very short time, and since this power loss is proportional to the square of the current, the FR loss in the coil decreases very rapidly as the current I in the coil decreases. This is to be compared with the continued and substantially constant peak FR loss in a solenoid driven from a power source as shown in FIG. I. To implement this feature it is important that the current pulse be compatible and tailored to the particular stroke length and time of travel so that the peak and tapering attain the desired operation.

In the solenoid of this invention it is usually necessary or desirable to latch the solenoid in the actuated position. To accomplish this, a latching current may be supplied by a second voltage power supply 46 coupled to coil 22 through switch 48 and diode 50. Diode 50 isolates the power supply 46 so as to prevent the discharge of capacitor 38 through this power supply upon closing both switches 12 and 48. However, when the voltage on coil 22 drops to a value substantially equal to the voltage of power supply 46, a clamping circuit is maintained in coil 22 by power supply 436. It should be noted that this current represents the current required to clamp the solenoid when the air gap in the solenoid is substantially zero and, therefore, this current need only be a small percentage of the maximum actuating current shown in FIG. 2b. Values of the clamping current required to clamp a solenoid in the fully actuated position will depend upon the permeability of the iron in the solenoid and the extent to which the solenoid gap is substantially zero. Characteristically, the clamping current required is only approximately 2 percent of the current required for actuation of the solenoid from the fully extended position. Therefore, the FR loss in the solenoid coil will be on the order of 0.04 percent of the FR loss incurred during the peak actuating current periods of operation of the solenoid. Consequently, the solenoid may be clamped in the actuated position for substantial periods of time without significant heating and power dissipation within the solenoid coil.

It is to be understood that other circuits may be used to create a current wave form similar to that shown in FIG. 2b, or at least to create a current wave form characterized by a rapid initial rise in current to a peak value followed by decay in current as the solenoid plunger moves to the actuated position and finally to stabilize the current value sufficient to clamp the solenoid in the actuated position for the time period desired. If the capacitor discharge system shown in FIG. 2 is used, the capacitor 38 and the voltage power supply 36 should be selected in conjunction with the characteristics of the solenoid so that the discharge of ca pacitor 38 through coil 22 is adequate to cause the desired peak value of current I and, if actuation speed is important, to result in a minimum rise time in the current wave form.

As previously mentioned, the current I as shown in FIG. 2b is decreased from its peak value to its value at time 1,. The physical event that makes this attainable may be attributed to the following. The decrease of the current in this region is due to the actual rate of change of the magnetic field in the solenoid which results in a counter-emf that decreases or tapers the current. This effect may be referred to as a [d(Li)/dt] effect. Thus, it is apparent that the FR energy loss in the solenoid may be decreased by decreasing the time during which peak or near peak currents exist in the solenoid coil, and this in turn may be accomplished by decreasing the solenoid actuation time since the above effect is time dependent.

Now referring to FIG. 3, another embodiment of the present invention may be seen. In this embodiment the solenoid is excited with the same electrical circuit as used in FIG. 2, the description of the operation of that circuit being directly applicable to the circuit of FIG. 3. However, in FIG. 3 the solenoid plunger 26 is connected to load 28 through a spring 52. (The interconnection of the load to a solenoid by a spring for load movement is referred to herein as load decoupling or spring coupling or decoupling.) Thus, the plunger 26 may move independent of the motion of the load 28 by storage of energy in spring 52. Upon excitation of the solenoid, plunger 26 is free to rapidly accelerate toward the stationary portion of the solenoid, thereby storing mechanical energy in spring 52 for subsequent and more leisurely delivery of the mechanical energy to the load 28. In this manner, the solenoid actuation time may be kept reasonably short so that the solenoid current may be quickly reduced to a latching value, thereby minimizing the PR loss in the solenoid. Such a spring coupling to the load 28 results in a gross improvement in solenoid efficiency, particularly for loads which by their nature are incapable of a quick response, such as fluid pumps and loads having a relatively high inertia.

Ideally, the plunger should experience a zero travel time and reach the stationary portion of the solenoid at zero velocity. This is physically impossible. However, the efficiency of the solenoid of FIG. 3 can be greatly improved by choosing the spring constant of the spring 52 so that plunger 26 is accelerated toward the stationary portion of the solenoid through approximately half the length of the stroke of the solenoid, at which point the spring force should become larger than the solenoid force so as to thereafter decelerate the plunger 26 so that the plunger arrives at the stationary portion of the solenoid with little kinetic energy. In this manner, most of the mechanical work done by the solenoid will be stored in the spring 52, rather than dissipated by the collision of the plunger with the stationary portion of the solenoid.

The above spring action and plunger interaction is illustrated in FIGS. 3a and 3b, which graphically present the various forces and the velocity of the plunger 26 upon actuation of the solenoid of FIG. 3 at various plunger positions. In these figures, it is assumed that there is very little motion of the load 28 within the small time required for actuation of the solenoid, though clearly if such an assumption were not substantially true, a spring having a different spring constant could be chosen so as to still achieve the operation about'to be described. It should also be noted that the notations on the figures fully actuated refers to a plunger position against the stationary part of the solenoid and fully extended refers to the at rest or starting plunger position before energization. Thus, in FIGS. 3a-d the abscissa is a plot of plunger position. The solenoid force (line 5d of FIG. 3a) may be relatively constant throughout the plunger travel, turning upward in the fully actuated position because of a collapse in the leakage fields, and similarly sloping downward at the fully extended position because of an increase in the leakage and fringing fields. The force of the spring 52 is shown as line 56, and linearly increases from the fully extended position of the plunger to a value somewhat under twice the solenoid average force at the fully actuated position. The imbalance in these two forces causes a velocity of plunger 26 as shown in FIG. 3b. The plunger accelerates from the fully extended position to point 58 where the spring force and the solenoid force are equal, and then decelerates to point 60 where it impacts the stationary portion of the solenoid with relatively little kinetic energy (since kineticenergy is proportioned to the square ofa velocity, an impact at 10 percent of the maximum velocity dissipates kinetic energy of only 1 percent of the maximum kinetic energy). For the more slowly reacting loads, such as fluid pumps or substantial inertias, the spring should be selected to the solenoid so as to store in excess of 75 percent or more of the total solenoid mechanical energy output if a particularly high efficiency is to be obtained. Thus, spring constant selection is one effective method for achieving matching. However, a spring is not absolutely necessary to achieve matching". Matching" can be achieved by proportioning the force developed by the solenoid to the load. Referring to FIG. 5, for no external load force on the armature, as in the previous case, the efficiency for producing output work is zero by definition. For an external load force equal to the magnetic force the acceleration of the armature is zero (no net forcel), the time for completion of stroke and therefore the Joule heating are infinite, and again the efficiency for output work is zero. For intermediate cases a finite efficiency is obtained, and for some matched conditions a maximum efficiency is obtained. This is suggested in FIG. 5. Thus, the maximum efficiency is obtained by taking only a portion of the available energy. Any effort to obtain more (or less) than the method portion of available energy results in lower efficiency.

It should be noted that in the fully actuated position the spring force exceeds the solenoid force, at least as shown in FIG. 3a, until there is sufficient motion of the load to substantially decrease the spring force. Consequently, to keep the solenoid in the fully actuated position during the time the energy stored in spring 52 is transferred to the load 28 there must be some method of latching the solenoid in this position. This may be achieved in a number of ways. An obvious method of achieving the desired latching is to provide a mechanical latching device to essentially catch the plunger 26 in the fully actuated position and to retain it in that position for the desired period. Such a scheme eliminates the need for any latching current in the solenoid coil and, at least theoretically, is a most efficient method of achieving the required latching. However, though mechanical latching may be suitable for some applications, the life, reliability and complexity of a mechanical latching scheme make it unsuitable for many applications.

One convenient latching system is illustrated in FIGS. 40 and 4b, which show on an expanded scale a portion of the stationary part of the solenoid and of the plunger 26 in the fully extended position and in the actuated position, respectively. The plunger face (or alternatively the face of the stationary part of the solenoid) is provided with a plurality of indentations 59, each having a depth equal to a small part of the air gap when the plunger is fully extended, and defining raised faces having a face width on the order of the depth of the indentations. The result achieved by use of the indentations is as follows. When the plunger 26 is fully extended, the depth of the indentations is small compared to the average air gap between the stationary portion and the plunger. Therefore, the magnetic field between the two portions of the solenoid is relatively uniform, the effective area of the solenoid being substantially equal to the projected areas of the facing surfaces of the solenoid. However, as the plunger approaches the fully actuated position, the air gap in the region of the indentations becomes large compared to the overall air gap, and finally when the plunger is in contact with the stationary portion of the solenoid as shown in FIG. 4b, the only significant air gap is in the region of the indentations in the plunger. Consequently, the field tends to concentrate within the raised areas of the plunger, thereby decreasing the effective area of the solenoid. In general, the solenoid force is equal to where is the flux between stationary portion 20 and plunger 26, n is the permeability of free space and A is the effective area over which the flux 4) is distributed. Thus, by decreasing the effective area of the solenoid during the last portion of the stroke of the solenoid, the solenoid force may be greatly increased at the end of the stroke so as to exceed the spring force 56 of FIG. 3a and latch the solenoid in the fully actuated position. Of course, the concentration of the flux as a result of the indentations tends to reduce the total flux below that which would be achieved with a flat faced plunger. However, this effect is fairly small since the concentration of the field within the iron is very localized (provided that the incremental permeability of the iron is not excessively low under these conditions). Also, in general, the collapse of the leakage fields as the plunger gap goes to zero is a further aid in increasing the force on the plunger at the fully actuated position for latching purposes.

Other methods of latching may also be used either alone or in conjunction with the last described method. By way of example, the current in the solenoid coil 22 may be increased by approximately 41 percent near the end of the plunger travel. This will have the effect of substantially doubling the solenoid force, thereby creating the desired clamping action. However, in this method the increase in flux in the iron is not localized, as it was for the indented plunger, and consequently, the saturation characteristics of the iron are most important. In general, the net effect of this method is that the solenoid output must be reduced somewhat so as to allow for the increase in flux density at the end of the travel.

Several other variants of the invention should be considered to fully appreciate the broad scope of the invention. It is apparent that if the rise time in the current wave form is very short (FIG. 2b), the full solenoid force will be available for accelerating the solenoid plunger 26 away from the fully extended position. However, as the solenoid begins to move toward the actuated position, the spring force increases so as to decrease the acceleration and subsequently even decelerate the plunger as it approaches the stationary portion of the solenoid. Consequently, it is clear that the spring partially resists the plunger motion, thereby increasing the length of time for plunger actuation compared to a solenoid having no load connected thereto. Of course, a solenoid with no load connected thereto would provide no useful output work since all the mechanical energy would be dissipated upon collision of the plunger with the stationary portion of the solenoid. However, a non-linear spring may be used for the spring 52 so as to effectively store most of the kinetic energy in the plunger just before the plunger arrives at the stationary portion of the solenoid. This is illustrated in FIGS. 30 and 3d.

In FIG. 3c the solenoid force 541 is the same as shown in FIG. 3a. However, the spring force represented by line 62 remains negligible throughout the first portion of travel of the plunger (i.e., near fully extended position), and rapidly increases to a value much higher than the solenoid force near the fully actuated position. Thus, the plunger is free to accelerate substantially unrestrained throughout most of the plunger motion with the non-linear spring suddenly storing the kinetic energy in the plunger just before the plunger strikes the stationary portion of the solenoid. In the extreme, the solenoid may operate essentially as an unloaded solenoid, with the kinetic energy which would normally be wasted by collision of the plunger with the stationary portion of the solenoid being stored in the spring at the end of the plunger travel. However, it should be noted that the latching problem using such non-linear springs becomes increasingly difficult because of the higher latching forces required, thereby somewhat limiting, for practical purposes, the extent of the non-linearity which may be used. (In that regard, it should be noted that a non-linear spring characterized by a decrease in stiffness at an increased displacement, though somewhat less efficient than a linear spring, is desirable in some applications because of a corresponding decrease in the latching force required).

Various types of non-linear springs suitable for such use are well-known in the prior art. By way of example, a diaphragm shaped spring has a non-linear characteristic suitable for such use, since the incremental spring rate of such springs increases rapidly as the spring is defiected from its flat condition. Similarly, a stiff coil spring which only comes in contact with the load as the plunger approaches the fully actuated position may be used. Though in such a situation there would be a slight time delay between excitation of the solenoid coil 22 and any motion of the load, the time or load actuation could be reduced to only a small fraction of the time required for the solenoid actuation. In this regard it should be noted that the use of even a linear spring for spring 52 in FIG. 3, in accordance with the invention, has in many casesresulted in load actuation times for a given solenoid shorter than the actuation times achieved by direct connection of the solenoid plunger 26 with the load 28.

In the extreme case, the plunger 26 is allowed to freely accelerate toward the stationary portion of the solenoid and just before impact therewith, the kinetic energy of the plunger is stored in the spring 52. In this case, the efficiency of the solenoid is given by the equation:

where 1,, is the efficiency for a solenoid having idealized non-linear coupling spring, E is the mechanical energy imparted to the plunger, and E J is the energy lost in Joule heating in the solenoid winding.

Assuming that there are no eddy current or friction losses, and making other reasonable assumptions as required, the efficiency is given by the following equation:

R is the resistance of the solenoid winding (ohms) S is the plunger stroke (meters) m is the mass of the plunger (kilograms) is the angle between the solenoid tractive surfaces and a line perpendicular to the direction of plunger motion (0 in FIGS. 1 & 3)

n is the number of turns in the solenoid winding A is the effective solenoid area (square meters) n 4" X 10 (Henries/meter) B is the gap magnetic field (Webers/square meter) It may be seen that the efficiency is highest if the parameter g is lowest. Thus, the resistance of the solenoid winding should be as low as possible, the stroke should be as short as possible consistent with the load actuation requirements, the mass of the plunger should be as low as possible and the angle 5 should be 0 (a flat faced plunger). On the other hand, the number of turns, the effective solenoid area, and the flux density in the solenoid area should be as high as possible (the parameter n /R is an approximate measure of the winding window area). Thus, flat faced tractive solenoids as shown in FIGS. 1 and 3, having a short stroke tend to be the most efficient solenoids. For a reasonable choice of solenoid parameters, the parameter g can be 0.l or less, and efficiencies as high as 95 percent are at least theoretically possible. This is to be compared with the efficiency achievable using a linear spring for spring 52 in FIG. 3 which as a result of a similar analysis is given by the equation:

where 17 is the efficiency for a solenoid having a linear coupling spring, as illustrated in FIGS. 3a and 3b. For the value of the parameter g equal to 0.1 the efficiency for the linear spring coupled solenoid is still theoretically over 94 percent and thus the increase in efficiency by using a non-linear spring is, at least in some applications, not warranted in lieu of the more severe problem of latching the solenoid in the fully actuated position and the characteristics of the motion imparted to the load on the solenoid. (The selection of the factors affecting g to maximize efficiency may be referred to as g optimization).

Now referring to FIG. 2 again, a further important consideration in the design of an efficient solenoid actuator (previously discussed in connection with FIG. 5) may be illustrated. In FIG. 2 the solenoid plunger 26 is directly connected to the load 28. Once the forcedisplacement characteristics of the load 28 are known, an expression for the efficiency of the solenoid similar to the preceding equations may be derived. By way of specific example and as an approximation, assume that the solenoid has an actuating force independent of plunger position, and similarly that the load also has such a constant force independent of the load position. Thus, the problem becomes one of selecting the size solenoid for the load force requirements to give the most efficient operation. At one extreme, if the solenoid force just equals the load force requirements, the time for completion of the stroke is infinite and similarly the FR loss in the solenoid coil will be infinite, thereby resulting in an efficiency of zero. At the other extreme, if the solenoid force is very large in comparison to the load force requirement, the amount of useful work delivered to the load will be very small in comparison to the kinetic energy dissipated by the collision of the plunger I/the stationary portion of the solenoid, again in the extreme yielding an efficiency of zero. Therefore, it may be seen that if high efficiency is to be achieved, even using the solenoid excitation circuit shown in FIG. 2, the solenoid must be properly matched to the load requirements. For the constant load-force requirement, it may be shown that the most efficient actuator will result if the load force requirement is approximately 80 percent of the solenoid force. In this case, the efficiency of the actuator is given by the equation:

where 1 is the efficiency for a solenoid coupled directly to a load having a constant load force requirement. For a g parameter equal to 0.1, the efficiency achievable is approximately 84 percent. This same concept of matching the characteristics of the solenoid to the force requirements of the load is equally applicable to loads having various force requirements and/or inertias, etc. to produce an actuator system having a maximum efficiency.

Thus, there has been described herein a number of methods, structures, circuits and apparatus for grossly increasing the efficiency of solenoid actuators, and for practicing the present invention. While prior art solenoids and the methods of mating the solenoid with the load to be driven thereby, and of exciting the solenoids typically yield efficiencies ranging from 0.1 to 5 percent, various configurations of solenoids and circuits have been herein disclosed which theoretically may yield efficiencies upwards of 95 percent. Solenoids designed and fabricated using the teachings of the present invention have verified the potential for such highly efficient operation. Solenoids have been fabricated using all the teachings of the present invention, and efficiencies of over 70 percent have been measured on these units. Of course, the principles of the present invention may be used with any of the well-known prior art solenoid configurations, including both linear and rotary actuators, though obvious modifications in the structure and circuits disclosed herein may be required or desirable depending upon the application.

As a further alternate, the principles of the present invention may be applied to solenoid generators for the conversion of mechanical energy into electrical energy. As with the solenoid actuators, such solenoid generators also have a high efficiency and result in a structurally simple apparatus for the conversion of short stroke mechanicalmotion into electrical energy.

One embodiment of the apparatus for achieving a solenoid generator is shown in FIG. 6. In this figure a C core solenoid is shown, though other solenoid forms may also be utilized. The solenoid plunger 70 is attached to one end of the coupling spring 72 through a plunger rod 74. The other end of the coupling spring 72 is attached to a mechanical driver 76 which provides the basic mechanical motion for the generator. (Any well known mechanism, preferably a reciprocating mechanism, may be used in this embodiment for the driving means, such as one in which a reciprocating source of mechanical energy naturally occurs, or one in which rotary motion is converted to a reciprocating motion, such as, by way of example, the well known combination of a crank shaft, connecting rod, and slide member to give linear reciprocating motion of the slide member.) A capacitor 78 is connected through a silicon controlled rectifier 80 to the winding on the stationary portion of the solenoid 82. Also connected across the winding is a diode 84 in series with the parallel combination of transistor 86 and resistor 88. Resistor 88 provides a leakage path so that the breakdown voltage of transistor 86 will not be exceeded when the transistor is first switched off. As shall be subsequently described in greater detail, silicon controlled rectifier 80 provides a triggerable switch in series with the storage capacitor 78 which will automatically open when the current through the silicon controlled rectifier goes to zero, and transistor switch 86 provides a switching means which may be turned on and off by an appropriate signal applied to the base of the transistor.

Now referring to FIGS. 7a through 7d, the sequence of operation of the apparatus of FIG. 6 may be seen. In these figures the silicon controlled rectifier 80 of FIG. 6 is schematically represented by switch 90 and transistor 86 is schematically represented by switch 92. In

FIG. 7a switch 90 is open and switch 92 is closed. Capacitor 78, the means used to store the electrical energy generated from the mechanical energy input, may or may not have a charge thereon. (In general, any electrical energy utilization means may be used in place of capacitor 78, including both energy storage and en- 7 ergy using means such as batteries, lights and the like.)

The coupling spring 72 is in the relaxed state, and the driving member 76 is in what will be referred to as the withdrawn position. In this state, the plunger lies against the stationary portion 82 of the solenoid. It is desirable to have a current flowing in the solenoid coil 94 which may be caused to flow through the diode trap 84 by the collapsing magnetic field in the solenoid or may be caused by an external voltage source (not shown) applied at terminal 96.

In FIG. 7b the current through the solenoid coil 94 is increased by application of the voltage at terminal 96 so as to latch the plunger 70 against the stationary portion 82 of the solenoid, and the driving member 76 has been mechanically forced to what will be referred to herein as the extended position, thereby compressing coupling spring 72 and storing a substantial amount of mechanical energy therein.

The current in solenoid coil 94 is thereafter allowed to decrease slightly so that the force exerted on plunger 70 by coupling spring 72 just overcomes the latching force between the stationary portion 32 and the plunger 70. For purposes of explanation only, it has been assumed that the latching is achieved by indentation of the pole faces as hereinbefore described so that as plunger 70 starts to move away from the stationary portion of the solenoid, the magnetic force initially drops rapidly from the latching force to the normal solenoid force of the solenoid. This isillustrated in FIG. 8, where the magnetic force and the spring force are plotted versus plunger position as the plunger moves from the position shown in FIG. 7b to the position shown in FIG. 70, that is, from the fully withdrawn position to the fully extended position. During the first portion of the motion, the spring force substantially exceeds the magnetic force and the plunger is accelerated away from the fully withdrawn position, reaching maximum velocity at the point at which the magnetic force equals the spring force. From there to the fully extended position, the plunger 70 decelerates, since the magnetic force exceeds the spring force during this time. Thus, through approximately one half of the plunger motion, the plunger is accelerated to a peak velocity and thereafter is decelerated so as to arrive at the position shown in FIG. 7c, that is, in the fully extended position, with little or no kinetic energy. This is achieved by matching the spring characteristics of spring 72 to the magnetic force characteristics of the solenoid. By way of example, to achieve this matching so that the plunger reaches the position shown in FIG. 7c with no kinetic energy, the area under the magnetic force curve, as shown in FIG. 8, should be equal to the area under the spring force curve. Thus, when the plunger reaches the fully extended position, it does so with zero (or in practice, nearly zero) velocity.

Referring again to FIG. 7b, when the latching force falls to a value equal to, or very slightly less than the spring force of the coupling spring 72, there still remains a high magnetic field in the solenoid core and, in fact, the majority of the core is near saturation (latching being achieved by such means as the high saturation level induced inthe pole faces by the local flux concentration caused by the pole face indentations as hereinbefore described). As the plunger moves to the position shown in FIG. 70, the flux in the solenoid core and in the plunger remains approximately constant, with the mechanical energy initially stored in coupling spring 72 (FIG. 7b) being converted into magnetic energy stored in the solenoid air gap (FIG. 7c). The relationship between the inductance of the solenoid coil and the current therein is given by the equation where L is the inductance of the coil,

N is the number of turns on the coil,

(1) is the flux linking of the coil, and

I is the current through the coil.

The inductance of the solenoid in the position shown in FIG. 7b is high, but the inductance of the solenoid as shown in FIG. 70 is low because of the large air gap in the magnetic path. Therefore, it is apparent that the current in the solenoid coil increases greatly as the plunger moves from the position shown in FIG. 7b to the position shown in FIG. 7c.

In practice, there is some collapse in the magnetic field as the plunger moves from the fully withdrawn position to the fully extended position; This collapse is caused by the fact that a voltage is required to maintain the current through the coil and through diode 84, with this required voltage being generated by the collapse of the magnetic field. Thus, the rate of collapse of the magnetic field may be determined from the equation where N equals the number of turns in the solenoid coil,

(Drb/dt) equals the time rate of collapse of the magnetic field in the solenoid,

l equals the solenoid current,

R equals the solenoid winding resistance and other resistances in the loop comprised of the switch 92 and diode 84 and the solenoid coil, and

V, equals the fixed voltage drops in the loop, such as the forward conduction voltage drop in diode 84.

It may be seen from this equation that the field collapse suffered as the plunger moves from the fully withdrawn position to the fully extended position depends on the length of time required for such motion and, to the extent that the motion is rapid, the amount of collapse in the field may be kept very low. Similarly, the energy dissipation due to iR loss and current flowing over fixed voltage drops, such as in diode 84, is time dependent and, therefore, the total energy lost through such dissipation depends on the length of time required for the plunger motion. Thus, there is a direct analogy between the use of coupling spring 72 and the matching of the coupling spring to the solenoid characteristics for the solenoid generator, as now being described, and the solenoid actuators and the coupling spring used therein, as hereinbefore described with reference to FIG. 3. In this regard, the concept of a solenoid g factor and g optimization for maximum efficiency, as that g factor appeared in the hereinbefore presented equations for efficiency of solenoid actuators, is also directly applicable to solenoid generators. Thus, by using the proper coupling spring 72 and keeping the solenoid latched until the driving member '76 is moved from the position shown in FIG. 7a to the position shown in FIG. 7b, and then unlatching the solenoid, the time required for the motion of the solenoid plunger may be caused to be very short in comparison with the time required for the motion of the driving member 76, with the net effect that the i R losses and other electrical losses are grossly reduced over that which would be incured by not using a coupling spring. (As before, the latching current is small, and therefore the i R loss during latching (FIGS. 7a and 7B) is almost negligible.) When the plunger arrives at the position shown in FIG. 70, the transistor switch 92 is immediately opened and SCR 90 is fired. (As implied, this may be achieved, by way of example, by a position sensor having a time response on the order of the time required for the motion of the plunger, or less, with the position sensor sensing the position of the plunger to turn off the transistor and pulse the SCR on by any one of the well known pulse circuits for driving an SCR.) Thus, the current circulating through the solenoid winding 94 charges the capacitor 78 as the solenoid field collapses (FIG. 7d). When the field collapses substantially to zero, the current charging capacitor. 78 also falls to zero, thereby turning off the silicon controlled rectifier 90. The time required for the field to collapse to zero and the energy in the field stored in capacitor 78 is very short, so that the total energy lost in the FR loss within the winding is a very small percentage of the energy stored in the capacitor. Of course, lamination of the solenoid core and plunger to minimize eddy current losses, the design of the structure so as to minimize hydrodynamic losses, and the minimization of friction losses are also important but well-known design considerations for such structures. Thus, it may be seen that mechanical energy is first stored in the coupling spring 72 which is then converted to magnetic energy stored in the magnetic field in the solenoid, and finally to electrical energy stored in capacitor 78. When silicon controlled rectifier 90 stops conducting, transistor switch 92 is closed, and the driving member 76 is returned to the withdrawn position, returning plunger to the latched condition as shown in FIG. 7a, thus completing the cycle of operation and returning the solenoid to the initial state for repeat of the cycle. (If a position sensor is used to sense the position of the plunger to operate the transistor switch and SCR, the transistor switch will close automatically as the plunger is returned to the withdrawn position.)

A number of solenoid generators, as shown in FIG. 6, may be used with a single electrical energy utilization means such as a capacitor storage means, the capacitor serving as a filter and energy storage device to provide a substantially'constant dc voltage output for the generating system. In this regard, it should be noted that the function of the solenoid generators is substantially unaffected by a voltage initially on capacitor 78 or by a concurrent charging or discharging of the capacitor due to a second solenoid generator or due to a load applied across the capacitor. Thus, a number of independently driven solenoid generators may be connected to the common storage capacitor as illustrated for a two solenoid system in FIG. 9. In such a system, the voltage ripple on the capacitor 78 may be reduced by phasing the operation of the two generators so that they alternately charge the storage capacitor.

Thus, while the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

We claim:

l. A method of generating electrical energy with a solenoid having a solenoid coil and a plunger, comprising the steps of:

a. causing a current flow in said solenoid coil to cause a substantial magnetic field in said solenoid;

b. causing said plunger to move from the withdrawn position to the extended position against the force of said magnetic field while allowing said current in said solenoid coil to increase in response thereto;

0. terminating said current in said solenoid coil and coupling said solenoid coil to an electrical energy utilization means to receive electrical energy as said magnetic field collapses.

2. A solenoid generator system comprising a solenoid having a plunger and a stationary member with a solenoid winding having two leads, a driving member, a coupling means and a circuit means coupled to said solenoid winding leads, said driving member being coupled to said plunger through said coupling means, said circuit means having a first switching means coupled between said leads for electrically coupling said leads and for controllably, substantially terminating current through said first switching means, and further having a second switching means in series with an electrical energy utilization means coupled between said leads.

3. The solenoid generator system of claim 2 wherein said electrical energy utilization means comprises a capacitor.

4. The solenoid generator system of claim 2 wherein said coupling means comprises a spring means so that said driving member may move relative to said load and store mechanical energy in said spring means.

5. The solenoid generator system of claim 4 wherein said spring has a spring constant matching the force developed by said solenoid.

6. The solenoid generator of claim 2 wherein said first switching means is coupled in series with a diode.

7. The solenoid generator of claim 6 wherein said first switching means is a transistor and said second switching means is a silicon controlled rectifier.

8. The solenoid generator of claim 2 wherein said electrical energy utilization system is a capacitor, said coupling means is a spring means having a spring constant matching the force developed by said solenoid, said first switching means is a transistor coupled in series with a diode, and said second switching means is a silicon controlled rectifier.

9. The method of generating electrical energy comprising the steps of:

a. providing a solenoid type device having a magnetic stationary member and a magnetic moving member movable between first and second orientations with respect to said stationary member, with said magnetic members defining at least a portion of a magnetic circuit which will result in the magnetic encouragement of said moving member to said first orientation upon the establishment of a magnetic field in said magnetic circuit;

b. providing at least one solenoid coil disposed so that a magnetic field in said magnetic circuit links said coil;

c. establishing a substantial magnetic field in said magnetic circuit when said moving member is in said first orientation;

d. forcing said moving member to said second orientation against the magnetic encouragement of said magnetic field while allowing current in one of said solenoid coils to increase in response thereto;

e. terminating said current and coupling one of said solenoid coils to an electrical energy utilization means to receive electrical energy resulting from the collapse of the magnetic field in said magnetic circuit.

10. The method of claim 9 wherein a mechanical energy storage means is provided to couple said moving member to a source of mechanical energy, and said moving member is rapidly forced to second orientation as a result of mechanical energy stored in said coupling means from the prior motion of said source of mechanical energy.

11. The method of claim 9 wherein current in one of said solenoid coils is allowed to increase in response to the forcing of the moving member to said second orientation by the substantially direct connection of the two leads of said one of said solenoid coils.

12. A method of generating electrical energy com prising the steps of:

a. providing asolenoid type device having a magnetic stationary member and a magnetic moving member movable between first and second orientations with respect to said stationary member, with said magnetic members defining at least a portion of a magnetic circuit which will result in the magnetic encouragement of said moving member to said first orientation upon the establishment of a magnetic field in said magnetic circuit;

b. providing a solenoid coil disposed so that a magnetic field in said magnetic circuit links said coil;

c. coupling said moving member to a source of mechanical energy through a spring means;

d. establishing a substantial magnetic field in said magnetic circuit when said moving member is in said first orientation and storing a substantial mechanical energy in said'spring means from said source of mechanical energy;

e. coupling the two leads of said solenoid coil together;

f. causing said moving member to rapidly move to said second orientation as a result of mechanical energy previously stored in said spring means;

g. uncoupling said two leads from each other and coupling said leads to an electrical energy utilization means.

13. The method of claim 12 wherein said spring means is selected in accordance with the mechanical energy required to move said moving member from said first orientation to said second orientation so as to result in the arrival of said moving member at said second orientation with a predetermined minimal kinetic energy.

14. A solenoid generator system comprising a solenoid having a moving member and a stationary member in part defining a magnetic circuit, a solenoid winding having two leads and coupling said magnetic circuit, and a circuit means coupled to said solenoid winding leads, said moving member being couplable to a source of mechanical energy, said circuit means having a first switching means coupled between said leads for electrically coupling said leads and for controllably, substantially terminating current through said first switching means, and further having a second switching means in series with an electrical energy utilization means coupled between said leads.

15. A solenoid generator system comprising:

first and second magnetic members adapted for relative motion between first and second relative positions, said first and second members forming at least a portion of a magnetic circuit, said first and second magnetic members being urged into said first relative positions when a magnetic field is established in said magnetic circuit;

a solenoid coil having first and second leads and couv pling said magnetic circuit;

means for establishing a substantial magnetic field in said circuit when said first and second members are in said first relative position;

means for coupling said first and second leads together when said first and second members are forced from said first relative position to said second relative position; and

means for decoupling said first and second leads from each other and coupling said leads to an energy utilization means.

16. The solenoid generator system of claim wherein said means for establishing a substantial magnetic field is a means for applying a magnetizing current to said solenoid coil.

17. The solenoid generator system of claim 15 further composed of a spring means, said first and second members being coupled to a source of mechanical energy, one of said first and second members being coupled to said source of said mechanical energy through said spring means.

18. Electrical generator apparatus comprising:

first and second solenoid members forming at least in part a magnetic circuit linking said members, and movable with respect to each other;

means for establishing a substantial magnetic field in said magnetic circuit;

means for maintaining a substantial field in said magnetic circuit as said first and second members are moved relative to each other in opposition to the magnetic attraction between said first and second members, said means including at least one conductive path linking said magnetic field and a means for allowing the current in said conductive path to increase; and

means for recovering electrical energy upon collapse of a magnetic field in said magnetic circuit. 19. A method of generating electrical energy comprising the steps of:

providing first and second solenoid members forming, at least in part, a magnetic circuit linking said members and movable with respect to each other, and a solenoid coil linking said magnetic circuit;

establishing a substantial magnetic field in said magnetic circuit;

maintaining a substantial field in said magnetic circuit as said first and second members are moved relative to each other in opposition to the magnetic attraction between said first and second members by allowing current in a conductive path linking said magnetic field to increase; and

coupling said solenoid coil to an electrical energy utilization means to recover electrical energy upon collapse of a magnetic field in said magnetic circuit. 

1. A method of generating electrical energy with a solenoid having a solenoid coil and a plunger, comprising the steps of: a. causing a current flow in said solenoid coil to cause a substantial magnetic field in said solenoid; b. causing said plunger to move from the withdrawn position to thE extended position against the force of said magnetic field while allowing said current in said solenoid coil to increase in response thereto; c. terminating said current in said solenoid coil and coupling said solenoid coil to an electrical energy utilization means to receive electrical energy as said magnetic field collapses.
 2. A solenoid generator system comprising a solenoid having a plunger and a stationary member with a solenoid winding having two leads, a driving member, a coupling means and a circuit means coupled to said solenoid winding leads, said driving member being coupled to said plunger through said coupling means, said circuit means having a first switching means coupled between said leads for electrically coupling said leads and for controllably, substantially terminating current through said first switching means, and further having a second switching means in series with an electrical energy utilization means coupled between said leads.
 3. The solenoid generator system of claim 2 wherein said electrical energy utilization means comprises a capacitor.
 4. The solenoid generator system of claim 2 wherein said coupling means comprises a spring means so that said driving member may move relative to said load and store mechanical energy in said spring means.
 5. The solenoid generator system of claim 4 wherein said spring has a spring constant matching the force developed by said solenoid.
 6. The solenoid generator of claim 2 wherein said first switching means is coupled in series with a diode.
 7. The solenoid generator of claim 6 wherein said first switching means is a transistor and said second switching means is a silicon controlled rectifier.
 8. The solenoid generator of claim 2 wherein said electrical energy utilization system is a capacitor, said coupling means is a spring means having a spring constant matching the force developed by said solenoid, said first switching means is a transistor coupled in series with a diode, and said second switching means is a silicon controlled rectifier.
 9. The method of generating electrical energy comprising the steps of: a. providing a solenoid type device having a magnetic stationary member and a magnetic moving member movable between first and second orientations with respect to said stationary member, with said magnetic members defining at least a portion of a magnetic circuit which will result in the magnetic encouragement of said moving member to said first orientation upon the establishment of a magnetic field in said magnetic circuit; b. providing at least one solenoid coil disposed so that a magnetic field in said magnetic circuit links said coil; c. establishing a substantial magnetic field in said magnetic circuit when said moving member is in said first orientation; d. forcing said moving member to said second orientation against the magnetic encouragement of said magnetic field while allowing current in one of said solenoid coils to increase in response thereto; e. terminating said current and coupling one of said solenoid coils to an electrical energy utilization means to receive electrical energy resulting from the collapse of the magnetic field in said magnetic circuit.
 10. The method of claim 9 wherein a mechanical energy storage means is provided to couple said moving member to a source of mechanical energy, and said moving member is rapidly forced to second orientation as a result of mechanical energy stored in said coupling means from the prior motion of said source of mechanical energy.
 11. The method of claim 9 wherein current in one of said solenoid coils is allowed to increase in response to the forcing of the moving member to said second orientation by the substantially direct connection of the two leads of said one of said solenoid coils.
 12. A method of generating electrical energy comprising the steps of: a. providing a solenoid type device having a magnetic stationary member and a magnetic moving member movabLe between first and second orientations with respect to said stationary member, with said magnetic members defining at least a portion of a magnetic circuit which will result in the magnetic encouragement of said moving member to said first orientation upon the establishment of a magnetic field in said magnetic circuit; b. providing a solenoid coil disposed so that a magnetic field in said magnetic circuit links said coil; c. coupling said moving member to a source of mechanical energy through a spring means; d. establishing a substantial magnetic field in said magnetic circuit when said moving member is in said first orientation and storing a substantial mechanical energy in said spring means from said source of mechanical energy; e. coupling the two leads of said solenoid coil together; f. causing said moving member to rapidly move to said second orientation as a result of mechanical energy previously stored in said spring means; g. uncoupling said two leads from each other and coupling said leads to an electrical energy utilization means.
 13. The method of claim 12 wherein said spring means is selected in accordance with the mechanical energy required to move said moving member from said first orientation to said second orientation so as to result in the arrival of said moving member at said second orientation with a predetermined minimal kinetic energy.
 14. A solenoid generator system comprising a solenoid having a moving member and a stationary member in part defining a magnetic circuit, a solenoid winding having two leads and coupling said magnetic circuit, and a circuit means coupled to said solenoid winding leads, said moving member being couplable to a source of mechanical energy, said circuit means having a first switching means coupled between said leads for electrically coupling said leads and for controllably, substantially terminating current through said first switching means, and further having a second switching means in series with an electrical energy utilization means coupled between said leads.
 15. A solenoid generator system comprising: first and second magnetic members adapted for relative motion between first and second relative positions, said first and second members forming at least a portion of a magnetic circuit, said first and second magnetic members being urged into said first relative positions when a magnetic field is established in said magnetic circuit; a solenoid coil having first and second leads and coupling said magnetic circuit; means for establishing a substantial magnetic field in said circuit when said first and second members are in said first relative position; means for coupling said first and second leads together when said first and second members are forced from said first relative position to said second relative position; and means for decoupling said first and second leads from each other and coupling said leads to an energy utilization means.
 16. The solenoid generator system of claim 15 wherein said means for establishing a substantial magnetic field is a means for applying a magnetizing current to said solenoid coil.
 17. The solenoid generator system of claim 15 further composed of a spring means, said first and second members being coupled to a source of mechanical energy, one of said first and second members being coupled to said source of said mechanical energy through said spring means.
 18. Electrical generator apparatus comprising: first and second solenoid members forming at least in part a magnetic circuit linking said members, and movable with respect to each other; means for establishing a substantial magnetic field in said magnetic circuit; means for maintaining a substantial field in said magnetic circuit as said first and second members are moved relative to each other in opposition to the magnetic attraction between said first and second members, said means including at least one conductive path linking said magneTic field and a means for allowing the current in said conductive path to increase; and means for recovering electrical energy upon collapse of a magnetic field in said magnetic circuit.
 19. A method of generating electrical energy comprising the steps of: providing first and second solenoid members forming, at least in part, a magnetic circuit linking said members and movable with respect to each other, and a solenoid coil linking said magnetic circuit; establishing a substantial magnetic field in said magnetic circuit; maintaining a substantial field in said magnetic circuit as said first and second members are moved relative to each other in opposition to the magnetic attraction between said first and second members by allowing current in a conductive path linking said magnetic field to increase; and coupling said solenoid coil to an electrical energy utilization means to recover electrical energy upon collapse of a magnetic field in said magnetic circuit. 